One of the problems known in the art to be associated with transmission of optical signals via optical network, is a problem known as dispersion. Typically, the optical output at the transmitting end is modulated and transmitted in its modulated form. However, in the optical network the beam undergoes light dispersion, which causes a distortion of the transmitted signal.
Various solutions were suggested in the past to overcome the dispersion problem. They included electronic methods used at the receiver and/or transmitter, and the use of high-dispersion optical elements located along the fiber link. U.S. Pat. No. 5,371,625 is one such publication that tries to address the dispersion problem. The publication discloses a frequency modulation technique used instead of the intensity modulation to increase the path of the transmission. However, this requires a suitable optical receiver at the receiving end.
U.S. Pat. No. 4,979,234 teaches the use of a saturated semiconductor laser amplifier that can impose a chirp upon optical pulses having a pulse repetition rate in the range of 8 to 16 GHz, and having an optical carrier wave of wavelength in the near infra-red range. This solution ensures that degradation of the pulses because of dispersion does not commence until after an initial portion of the fiber segment has been traversed by the propagating pulses.
As known in the art, a temporal self-imaging effect in single mode fibers (also known as TALBOT effect) can be applied to reflection of periodic signals, from linearly chirped fiber gratings. This effect can be used for multiplying the repetition frequency of a given periodic pulse train without distorting the individual pulse characteristics. For a given fiber, the practical limit on the frequency multiplication factor depends only on the temporal width of the individual pulse.
Furthermore, a combination of techniques for short pulse mode generation such as pulse mode locking and the self-imaging effects allows to obtain short pulse trains with ultrahigh repetition rates, in the terabit regime as described for example in “Temporal self-Imaging in single mode fibers”, T. Jannson and J. Jannson, JOSA-A Vol. 71, No. 11, 1393–1376, November (1981); “Technique for multiplying the repetition rates of periodic trains of pulses by means of a temporal—self imaging effect in chirped fiber gratings”, J. Azanz and M. A. Muriel, Opt. Lett. Vol, 24, No. 23, 16721674, (1999); “Quasi Self Imaging using apreiodic sequences”, G. Indebetouw, JOSA-A Vol. 9, No. 4, 549–558, November (1992). The disclosures of all references mentioned above and throughout the present specification are hereby incorporated herein by reference.